Ferroelectric polymers are of interest as most promising electroactive materials. Flexible transducers from ferroelectric polymer thin film with underneath semiconducting polymer active layer for high sensitive and versatile detection of physiological signals are described. When attached directly on the wrist, the flexible transducers can distinguish the transient pulse waves non-invasively and in situ, due to their fast response (milliseconds) and high sensitivity (down to several Pascal) to instantaneous change of blood pressure. High-resolution picture of one pulse wave is available to provide two most common parameters for arterial stiffness diagnosis. The transducers are also suitable for dynamic recognizing physiological signals under both physical exercise and medicine treatment, demonstrating their enormous potential for warning the risk of cardiovascular disease, and evaluating the efficacy of heart medicines. The transducers are easy to carry around with an operating voltage of 1 V and the power consumption less than 1 μW. Thus, they are valuable for applications like electronic skin and mobile health monitoring.

Industrial processing of polymeric materials normally involves fast cooling. We employed a commercial chip calorimeter (Flash DSC) to investigate the crystallization and annealing behaviors of poly(vinylidene fluoride) (PVDF) under fast cooling towards low temperatures. The corresponding polymorphic crystalline phases were identified by wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The results demonstrated that a cooling process faster than −500 K s⁻¹ results in major thick α-phase crystallites at high temperatures; in addition, subsequent isothermal annealing at low temperatures slowly generates minor thin β-phase crystallites rich with trans conformation. Our observations facilitate a better understanding of structural optimization during PVDF processing for its ferroelectric and piezoresponse performance in versatile applications. © 2016 Society of Chemical Industry

High-capacity or high-power-density capacitors are being actively investigated for portable electronics, electric vehicles, and electric power systems. The dielectric nanocomposite with a small loading of carboxylic polystyrene (PS-COOH) nanoparticles in poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] matrix, followed by chemical crosslinking has been described. Combination of these two methods significantly improved the capacity of electric energy storage at low electric field. Specially, the nanocomposite with 2 wt % nanoparticles and 15 wt % crosslinking agent achieved a dielectric constant of 17.2 and a discharged energy density of 17.5 J/cm³ (4.9 Wh/L) at an electric field as high as 324 MV/m, while corresponding values for pristine P(VDF-CTFE) are 9.6 and 13.3 J/cm³ (3.7 Wh/L), respectively. Fundamental physics underlying the enhancement in the performance of the nanocomposites with respect to P(VDF-CTFE) is illustrated by solid-state ¹⁹F nuclear magnetic resonance of direct excitation or ¹⁹F{¹H} cross polarization. It revealed different dynamics behavior between crystalline/amorphous regions, and PS-COOH nanoparticles favored the formation of polar γ-form crystals. Small-angle X-ray scattering studies revealed the contribution of the interface to the extraordinary storage of electric energies in the nanocomposites. This approach provided a facile and straightforward way to design or understand PVDF-based polymers for their practical applications in high-energy-density capacitors. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1160–1169

Ferroelectric vinylidene fluoride-trifluoroethylene copolymer [P(VDF-TrFE)] free-standing ultrahigh density (≈75 Gb inch⁻²) nanodot arrays are successfully fabricated through a facile, high-throughput, and cost-effective nano-imprinting method using disposable anodic aluminum oxide with orderly arranged nanometer-scale pores as molds. The nanodots show a large-area smooth surface morphology, and the piezoresponse in each nanodot is strong and uniform. The preferred orientation of the copolymer chains in the nanodot arrays is favorable for polarization switching of single nanodots. The ferroelectric polymer memory prototype can be operated by a few volts with high writing/erasing speed, which comply with the requirements of integrated circuit. This approach provides a way of directly writing nanometer electronic features in two dimensions by piezoresponse force microscopy probe based technology, which is attractive for high density data storage.

The electrostatic complexes of single-stranded deoxyribonucleic acid (ssDNA) and a cationic conjugated polyelectrolyte (CPE), poly{9,9-di[3-(1-ethyl-1,1-dimethyl ammonio)propyl]-2,7-fluorenyl-alt-1,4-phenylene dibromide} (PFN), were investigated. Fluorescence emission of PFN solution (10 μmol/L) can be drastically quenched to about one fourth of its original intensity in the presence of a trace amount (2.6 μmol/L) of ssDNA. The effect of oligonucleotide length on the fluorescence quenching behavior was also investigated. In contrast to single-stranded DNA with 20 bases (ssDNA-20), ssDNA with 40 bases (ssDNA-40) induces a relatively higher quenching efficiency and larger red-shift of PFN emission maximum. The binding constant of ssDNA-20 and PFN is estimated to be 1.12 × 10²¹. At extremely low concentration (10 nmol/L), PFN can respond to 0.2 nmol/L (or 2 × 10⁻¹⁰ mol/L) of ssDNA-20 by significant enhancement of its emission intensity. The result is contrary to the observation in the relative higher concentration, and its mechanism is postulated. Based on the high binding ability of ssDNA with cationic CPE, a label-free method for ssDNA detection is designed. It uses an electrostatic complex of cationic PFN and an anionic CPE, which exhibits fluorescence resonance energy transfer (FRET) between the two components. Addition of ssDNA improves the FRET extent, indicated by obvious change of fluorescence spectra of the conjugated polyelectrolyte complex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Conductive nanofibers are adopted to enhance the electric properties of ferroelectric polymers. Polyaniline (PANI) nanofibers doped by protonic acids have a high dispersion stability in vinylidene fluoride-trifluoroethylene copolymers [P(VDF-TrFE)] and lead to percolative nanocomposites with enhanced electric responses. About a 50-fold rise in the dielectric constant of the ferroelectric polymer matrix has been achieved. Percolation thresholds of the nanocomposites are relevant to doping levels of PANI nanofibers and can be as low as 2.9 wt% for fully doped nanofibers. The interface between the conductive nanofiber and the polymer matrix plays a crucial role in the dielectric enhancement of the nanocomposites in the vicinity of the percolation threshold. Compared with other dopants, perfluorosulfonic acid resin is better at improving the performance of the nanofibers in that it serves as a surface passivation layer for the conductive fillers and suppresses leakage current at low frequency. The nanofibers drastically reduce the electric field strength required to switch spontaneous polarization of P(VDF-TrFE). The nanocomposites can be utilized for potential applications as high energy density capacitors, thin-film transistors, and non-volatile ferroelectric memories.

A cationic water-soluble poly(p-phenylene vinylene) derivative (poly{2-methoxy-5-[3-(N,N,N-ethyldimethylamino)-1-propoxy]-1,4-phenylene vinylene}bromide) was synthesized by a facile approach. The fluorescence of the conjugated polyelectrolyte was enhanced in the presence of an anionic surfactant because of the regularity of the chain conformation. Meanwhile, its emission was efficiently quenched by a trace amount (10⁻⁶ mol/L) of the iron complex Fe(CN) with pronounced quenching efficiency. The cationic conjugated polymer chains were readily assembled on the surface of negatively charged CdTe quantum dots through electrostatic attraction. The resulting nanocomposites facilitated the charge transfer between the conjugated polymers and the quantum dots because of the extensive interfacial area and intimate contact of the two components. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008